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The impact of salt and sediment density stratification on vertical turbulent mixing in the Yangtze River Estuary
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摘要:
为研究河口水域盐和泥沙的垂向密度分层对垂向紊动扩散的影响，基于长江口北槽12.5 m深水航道南侧的实测水沙盐资料，分析长江口北槽水域的盐度及含沙量垂向分布特征，并利用Richardson数和PP81方案的零方程模型计算垂向紊动扩散系数，研究北槽水域盐和泥沙的垂向密度分层对垂向紊动扩散的影响。结果表明：盐和泥沙垂向密度分层影响下，长江口北槽河段沿程水体的垂向紊动扩散系数由近底层向近表层增大，水体中盐和泥沙等物质的垂向密度分层在北槽中下游河段对水体垂向紊动扩散产生较为明显的抑制作用；盐的垂向密度分层对水体垂向紊动扩散系数的抑制影响程度为大潮小于小潮、涨潮大于落潮；泥沙垂向密度分层的抑制影响为大潮大于小潮、涨潮大于落潮；盐的垂向密度分层是抑制水体垂向紊动扩散的主要因素，清水和盐水条件下的垂向紊动扩散系数比值最大可达5；泥沙的抑制作用相对较弱，清水和浑水条件下的水体垂向紊动扩散系数比值最大为2，垂向紊动抑制影响最大区域出现在近底层；盐和泥沙综合作用下的垂向密度分层，对物质垂向紊动扩散抑制程度更为明显，抑制前后物质垂向紊动扩散系数的比值在北槽中段的近底层达到最大值（约22）。
Abstract:This study examines vertical density stratification of salt and sediment in estuaries. Data were analyzed from the south side of a 12.5 m deep channel along the north channel of the Yangtze Estuary, including water, salt and sediment measurements. The overall distribution characteristics of salt and sediment content in the north channel waters were analyzed. The vertical turbulent diffusion coefficient was calculated using the Richardson number method and PP81 zero-equation model. This investigated the effect of vertical salt and sediment density stratification on vertical turbulent diffusion in the north channel waters. Results show the diffusion coefficient increases from near-bottom to near-surface layers with stratification. Stratification has a more pronounced inhibitory effect in the middle and lower reaches. Salt stratification results in less inhibition during spring than neap tides, and less during flood than ebb tides. Sediment stratification causes more inhibition during spring than neap tides, and more during flood than ebb tides. Salt stratification is the primary inhibitory factor, with coefficients up to 5 times lower under salt versus clear water. Inhibition by sediment is weaker, with coefficients up to 2 times lower under mud versus clear water, and strongest inhibition in near-bottom layers. Combined salt and sediment stratification more markedly inhibits material diffusion, with maximum coefficients of around 22 times lower in near-bottom mid-channel areas.
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图 7 无紊动抑制下的水体垂向紊动扩散系数
Figure 7. Water vertical turbulent diffusivity without turbulence suppression
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图 8 紊动抑制下的水体垂向紊动扩散系数
Figure 8. Water vertical turbulent diffusivity with turbulence suppression
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图 9 清水与盐水的水体垂向紊动扩散系数比值
Figure 9. Ratio of vertical turbulent diffusivity in clear water vs salt water
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图 10 清水与浑水的水体垂向紊动扩散系数比值
Figure 10. Ratio of vertical turbulent diffusivity in clear water vs muddy water
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图 11 紊动抑制前后水体垂向紊动扩散系数比值
Figure 11. Ratio of vertical turbulent diffusivity before and after turbulence suppression
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图 12 近底层水体垂向紊动扩散系数比值
Figure 12. Ratio of vertical turbulent diffusivity in the near-bottom layer
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图 13 紊动抑制下的物质垂向紊动扩散系数
Figure 13. Vertical turbulent diffusivity of materials with stratification effects
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图 14 紊动抑制前后物质垂向紊动扩散系数的比值
Figure 14. Ratio of material vertical turbulent diffusivity before and after turbulence suppression
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图 15 各站点物质垂向紊动扩散系数
Figure 15. Vertical turbulent diffusivity profiles at measurement stations
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